Generally, thermal recording materials are obtained by forming a thermal recording layer on a substrate, and the thermal recording layer contains an electron-donating generally colorless or light-colored dye precursor and an electron-accepting developer as main components. Thermal recording materials give an image to be recorded by an instant reaction between the dye precursor and the developer upon heating with a thermal head, a thermal pen or a laser beam. The above thermal recording materials have advantages that a recording is obtained with a relatively simple device, that the maintenance of the device is easy and that noise is not made much. Such thermal recording materials are therefore used in broad fields including a measuring meter, a facsimile machine, a printer, a computer terminal, a label printing machine, a ticket or card-issuing machine, and the like.
In recent years, particularly, thermal recording materials are used as receipts for gas, water and electric bills, ATM slips of banking facilities, various receipts, accounting recording sheets, thermal recording labels for POS systems, or thermal recording tags.
Use fields and demands of thermal recording materials are variously diversified, and environments in which such thermal recording materials are used are also diversified. Particularly, thermal recording materials are required to have heat resistance in storage under high-temperature environments at 80 to 100° C., particularly, in a car, a microwave oven, and further, they are required to have light resistance in storage outdoors or indoors or light resistance to sunlight through window or to a fluorescent lamp. On the other hand, there are also demands for thermal recording materials having excellent thermal response to a small energy in order to comply with decreased power consumption or rapid printing.
Thermal recording materials excellent in heat resistance in storage are disclosed in JP-A-10-35109 and JP-A-10-264525. However, the thermal recording materials are not satisfactory with regard to heat resistance in storage in an environment at 100° C. and also have low thermal response. As a method of improving the light resistance in storage, Japanese Patent No. 2727234 describes a method in which a specific anti-oxidant and ultraviolet absorbent are added. However, it cannot be said that sufficient light resistance in storage can be obtained.
Further, thermal recording materials prepared in the form of a thermal recording label or thermal recording tag are stored in high-temperature high-humidity environments in many cases, and the thermal recording materials are therefore particularly required to have high whiteness not only on a recorded image but also on a ground and are required to cause almost no change in such an image and ground.